Deliquescence process

The life persistency of a smoke cloud is deterrnined chiefly by wind and convection currents in the air. Ambient temperature also plays a part in the continuance or disappearance of fog oil smokes. Water vapor in the air has an important role in the formation of most chemically generated smokes, and high relative humidity improves the performance of these smokes. The water vapor not only exerts effects through hydrolysis, but it also assists the growth of hygroscopic (deliquescent) smoke particles to an effective size by a process of hydration. Smoke may be generated by mechanical, thermal, or chemical means, or by a combination of these processes (7). 

For some non-ferrous metals (copper, lead, nickel) the attack by sulphuric acid is probably direct with the formation of sulphates. Lead sulphate is barely soluble and gives good protection. Nickel and copper sulphates are deliquescent but are gradually converted (if not leached away) into insoluble basic sulphates, e.g. Cu Cu(OH)2)3SO4, and the metals are thus protected after a period of active corrosion. For zinc and cadmium the sulphur acids probably act by dissolution of the protective basic carbonate film. This reforms, consuming metal in the process, redissolves, and so on. Zinc and cadmium sulphates are formed in polluted winter conditions whereas in the purer atmospheres of the summer the corrosion products include considerable amounts of oxide and basic carbonate. ... 

Chameides, W. L. and Stelson, A. W. (1992). Aqueous-phase chemical processes in deliquescent sea-salt aerosols a mechanism that couples the atmospheric cycles of S and sea salt. /. Geophys. Res. 97, 20565-20580. 

In fact, Roger Bacon s formula was not too dissimilar from early Chinese recipes. But being natural products, all three ingredients were of variable purity. For example, the crude Indian or Chinese saltpetre was richer in true saltpetre than the European material, but all required recrystallisation. The preferred process seems to have involved wood ashes, containing potassium carbonate, which precipitated deliquescent calcium salts from the saltpetre solution. The solution was then passed through a filter, boiled to reduce the volume of water and then left until the transparent plates of purified saltpetre were formed. 

Chameides, W. L., and A. W. Stelson, Aqueous-Phase Chemical Processes in Deliquescent Seasalt Aerosols, Ber. Bunsenges. Chem., 96, 461-470 (1992a). 

Deliquescence.—It sometimes happens that a salt that has been crystallized and spread in the air to dry absorbs water instead of losing it and in time passes again into solution. This may occur with anhydrous salts as well as with hydrates but not so frequently. This conduct is readily understood if it is remembered that the process of drying is always dependent upon the equilibrium between the aqueous vapor pressure of the material undergoing drying and the partial pressure of the water vapor in the air. The vapor pressure of a salt solution is always lower than that of the pure solvent. When the solution is very concentrated, its vapor pres-... 

When, therefore, crystals of very soluble salts are drained and exposed to air, the mother liquor adhering to them tends to become diluted by absorption of atmosphere moisture. Some of the solid will then dissolve to saturate the dilute solution, and this process may finally carry all of the solid into solution. Deliquescence is therefore not to be attributed to any chemical affinity for moisture on the part of the salt but to its great solubility. Any very soluble salt is likely to be deliquescent, and a moderately soluble one will not be so. 

The above results indicate that a requirement for water photolysis by Pt/Ti02 is to prevent the reverse reaction on Pt sites. Wagner and Somoijai8) successfully carried out gas-phase water photolysis by Pt/SrTi03-crystal coated with deliquescent basic materials. Their method is reasonable to suppress the reverse reaction, because a deliquescent material coated on a substrate absorbs a large amount of water to form a thin film of its aqueous solution. The film inhibits the reaction products to readsorb directly on the catalyst, while the products on the catalyst can escape to the gas phase by diffusion, it is very important that H2 and 02 can desorb from the catalyst surface to the gas phase without making bubbles, because if they desorb as bubbles then they would inevitably mix with each other in the growing process of bubbles and recombine on Pt sites. In addition, an aqueous basic solution would work as an electrolyte which enhances ion transfer in photoelectrochemical reactions. 

Moist iodine vapor rapidly corrodes metals, including most stainless steels. The initial process is the formation of corrosion centers where small amounts of metal iodide are formed which deliquesce, and the corrosion then takes place electrochemically (41,42). Only titanium and molybdenum steels are unattacked by iodine (42,43). The corrosion of molten iodine has also been studied. 

With some substances, not necessarily salt hydrates, the reverse of efflorescence occurs. For example, if anhydrous calcium chloride is left in the air, it absorbs water vapour and eventually forms a very concentrated solution. This process is called deliquescence, and substances which behave like this are said to be deliquescent. Solid sodium hydroxide will deliquesce. 

Wet deposition processes depend mostly on microphysical properties of the aerosol, cloud formation, conversion of cloud droplets into rain drops, sedimentation, and evaporation of rain (Kanakidou et al., 2005). Recently, Gysel et al. (2004) discussed the deliquescence properties of water-soluble organic matter and how they affect the hygroscopic growth of atmospheric OAs. Depending on the chemical... 

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